1. Field of the Invention
The invention relates to a magnetic transducer, a thin film magnetic head using the same, and a method of manufacturing the same.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk drive. A composite thin film magnetic head, which has a stacked structure comprising a reproducing head having a magnetoresistive element (hereinafter sometimes referred to as an MR element) that is a type of magnetic transducer and a recording head having an inductive magnetic transducer, is widely used as the thin film magnetic head.
MR elements include an AMR element using a magnetic film (an AMR film) exhibiting an anisotropic magnetoresistive effect (an AMR effect), a GMR element using a magnetic film (a GMR film) exhibiting a giant magnetoresistive effect (a GMR effect), and so on.
The reproducing head using the AMR element is called an AMR head or simply an MR head, and the reproducing head using the GMR element is called a GMR head. The AMR head is used as the reproducing head whose surface recording density exceeds 1 gigabit per square inch, and the GMR head is used as the reproducing head whose surface recording density exceeds 3 gigabits per square inch. As the GMR film, a xe2x80x9cmultilayered type (antiferromagnetic type)xe2x80x9d film, an xe2x80x9cinductive ferromagnetic typexe2x80x9d film, a xe2x80x9cgranular typexe2x80x9d film, a xe2x80x9cspin valve typexe2x80x9d film and the like are proposed. Of these types of films, the spin valve type GMR film is considered to have a relatively simple structure, to exhibit a great change in resistance even under a low magnetic field and to be suitable for mass production.
FIG. 54 is a sectional side view of a general structure of a composite thin film magnetic head 800 (hereinafter simply referred to as a thin film magnetic head) using an MR element using a spin valve type GMR film (hereinafter referred to as a spin valve film). The thin film magnetic head 800 has a substrate 801 made of, for example, Al2O3. TiC (altic). A bottom shield layer 803 made of a magnetic material is stacked on the substrate 801 with an insulating layer 802 made of, for example, Al2O3 (alumina) in between. A bottom shield gap layer 804 and a top shield gap layer 806 made of, for example, Al2O3 or AlN (aluminum nitride) are stacked on the bottom shield layer 803. A stack 805, which is the above-mentioned spin valve film, is buried between the bottom shield gap layer 804 and the top shield gap layer 806.
A top shield layer 807 (also serving as a bottom pole) made of a magnetic material is formed on the top shield gap layer 806. A top pole layer 810 is located facing the top shield layer 807 with a write gap layer 808 made of, for example, Al2O3 in between. Thin film coils 811 buried in an insulating layer 809 are formed between the top shield layer 807 and the top pole layer 810. The bottom shield layer 803, the bottom shield gap layer 804, the stack 805 and the top shield gap layer 806 compose a reproducing head for reading out information from a magnetic recording medium. The top shield layer 807, the write gap layer 808, the insulating layer 809, the top pole layer 810 and the thin film coils 811 compose a recording head for writing information on the magnetic recording medium. A surface indicated by reference symbol S in FIG. 54 corresponds to a medium facing surface (an air bearing surface: ABS) of the thin film magnetic head 800 facing the magnetic recording medium such as a hard disk.
The structure of the stack 805 which is the spin valve film will be described with reference to FIGS. 55 and 56. FIG. 55 is a cross sectional view of the stack 805 parallel to the medium facing surface S (i.e., a cross sectional view taken along the line LVxe2x80x94LV of FIG. 54). FIG. 56 is a cross sectional view of the stack 805 perpendicular to the medium facing surface S (i.e., an enlarged view of the stack 805 shown in FIG. 54). The spin valve film is basically composed of a multilayered film having a stacked structure comprising four layers: an antiferromagnetic layer 851 made of, for example, PtMn (platinum-manganese alloy); a pinned layer 852 which is a magnetic layer made of, for example, Co (cobalt); a nonmagnetic metal layer 853 made of, for example, Cu (copper); and a free layer 854 made of, for example, NiFe (permalloy). When heat treatment takes place at, for example, 250 degrees centigrade in a state in which the pinned layer 852 and the antiferromagnetic layer 851 are stacked, the orientation of magnetization of the pinned layer 852 is fixed in, for example, the direction indicated by reference symbol Y in FIG. 56 by an exchange anisotropic magnetic field generated by exchange coupling occurring on an interface between the antiferromagnetic layer 851 and the pinned layer 852. Since the free layer 854 is separated from the antiferromagnetic layer 851 by the nonmagnetic metal layer 853, the orientation of magnetization thereof is not fixed but changes in accordance with an external magnetic field.
Reproduction of information in the MR element using the above-mentioned spin valve film, i.e., detection of a signal magnetic field from the magnetic recording medium is performed in the following manner. First, a sense current, which is a constant direct current, is passed through the pinned layer 852, the nonmagnetic metal layer 853 and the free layer 854 in, for example, the direction indicated by reference symbol X in FIG. 55. On receiving the signal magnetic field from the magnetic recording medium, the orientation of magnetization of the free layer 854 changes. Electrical resistance changes in accordance with a relative angle between the orientation of magnetization of the free layer 854 and the (fixed) orientation of magnetization of the pinned layer 852, and thus information is detected as a voltage change caused by a change in electrical resistance.
Generally, a distance between the medium facing surface S of the MR element and the opposite surface is called an MR height (MR-H). In the case of the MR element using the spin valve film, the MR height is determined in accordance with the distance between the medium facing surface S of the free layer and the opposite face. A read track width Tw of the MR element decreases as a recording density increases. Also, the MR height of the MR element tends to decrease as the read track width decreases. For example, the MR height is equal to 0.6 xcexcm when the read track width of the MR element is equal to 1 xcexcm, while the MR height is equal to 0.3 xcexcm when the read track width of the MR element is equal to 0.5 xcexcm.
As described above, a size reduction of the MR element advances. However, with the advance in the size reduction, the following problem arises due to heat generated in the MR element. That is, heat generated in the MR element is dissipated into the top and bottom shield layers (the shield layers 803 and 807 shown in FIG. 54) through the top and bottom shield gap layers. However, when the reproducing track width and the MR height of the MR element are reduced, a heat dissipation area of the MR element (i.e., the product of the reproducing track width and the MR height) is considerably reduced. Heat generation by the MR element incident to the reduction in the heat dissipation area becomes a factor that causes electro migration (a phenomenon in which a local void is created because of metal atoms migrating through a conductor) or interlayer diffusion. As a result, a problem exists: the longevity of the MR element decreases.
Japanese Patent Application Laid-open Nos. Hei 6-223331 and 10-222816 disclose a technique in which layers (a shield layer, an insulating layer, a substrate, etc.) around an MR element are made of a material having high thermal conductivity so that heat generated in the MR element is efficiently dissipated. However, when the heat dissipation area of the MR element decreases with the above-mentioned size reduction of the MR element, the improvement in efficiency of heat dissipation cannot be expected much even if the layers around the MR element have high thermal conductivity.
The invention is designed to overcome the foregoing problems. It is an object of the invention to provide a magnetic transducer, a thin film magnetic head and a method of manufacturing the same which can improve efficiency of heat dissipation.
A magnetic transducer of first aspect of the invention comprises: a nonmagnetic layer; a soft magnetic layer formed adjacent to one surface of the nonmagnetic layer and having the orientation of magnetization freely changing in accordance with an external magnetic field; a ferromagnetic layer formed adjacent to the other surface of the nonmagnetic layer; and an antiferromagnetic layer formed adjacent to a surface of the ferromagnetic layer, the surface being opposite to a surface in contact with the nonmagnetic layer, wherein the soft magnetic layer, the nonmagnetic layer, the ferromagnetic layer and the antiferromagnetic layer are configured so that one end surface thereof forms a surface facing the external magnetic field, and a distance between the one end surface of the antiferromagnetic layer and the opposite surface is longer than at least a distance from the one end face of the soft magnetic layer to the opposite face.
In the magnetic transducer of first aspect of the invention, electrical resistance changes in accordance with a change in the orientation of magnetization of the soft magnetic layer due to the external magnetic field (e.g., a signal magnetic field from a recording medium or the like). Thus, magnetic information is detected in accordance with a voltage change (a read output) incident to the change in resistance. Joule""s heat generated by a sense current passing through the magnetic transducer is dissipated through the antiferromagnetic layer having the longer distance between the one end face and the opposite face.
Preferably, a difference between the distance between the one end face of the antiferromagnetic layer and the opposite face and the distance between the one end face of the soft magnetic layer and the opposite surface is from 0.05 xcexcm to 1.0 xcexcm inclusive. When the difference between the distances is less than 0.05 xcexcm, a heat dissipation effect is little improved. When the difference between the distances is more than 1.0 xcexcm, asymmetry of a plus output and a minus output of the read output increases.
Moreover, the surface opposite to the one end face of the soft magnetic layer, the nonmagnetic layer, the ferromagnetic layer and the antiferromagnetic layer may be inclined to the one end face. The formation of the inclined surface makes it possible to obtain with relative ease the above-described configuration in which the distance between the one end face of the antiferromagnetic layer and the opposite face is longer than at least the distance between the one end face of the soft magnetic layer and the opposite face.
Moreover, the face opposite to the one end face of the soft magnetic layer may be parallel to the one end face, and the surface opposite to the one end face of the nonmagnetic layer, the ferromagnetic layer and the antiferromagnetic layer may be inclined to the one end face. When each end face of the soft magnetic layer is vertical as described above, an MR height can be more precisely determined.
A thin film magnetic head of first aspect of the invention comprises a magnetic transducer including: a nonmagnetic layer; a soft magnetic layer formed adjacent to one surface of the nonmagnetic layer; a ferromagnetic layer formed adjacent to the other surface of the nonmagnetic layer; and an antiferromagnetic layer formed adjacent to a surface of the ferromagnetic layer, the surface being opposite to a surface in contact with the nonmagnetic layer, wherein the soft magnetic layer, the nonmagnetic layer, the ferromagnetic layer and the antiferromagnetic layer are configured so that one end face thereof forms a surface facing a recording medium, and a distance between the one end face of the antiferromagnetic layer and the opposite face is longer than at least a distance from the one end face of the soft magnetic layer and the opposite face.
Preferably, the thin film magnetic head of first aspect of the invention further comprises two magnetic shield layers located so as to face each other with the magnetic transducer in between, for magnetically shielding the magnetic transducer. In this case, Joule""s heat generated in a magnetoresistive film is transferred to one magnetic shield layer through the antiferromagnetic layer.
Moreover, the thin film magnetic head of first aspect of the invention may have: two magnetic layers magnetically coupled to each other and each having a recording-medium-facing part including a magnetic pole, the magnetic poles facing each other with a gap layer in between, the magnetic layers being each formed of at least one layer; and thin film coils arranged between the two magnetic layers. A current is passed through the thin film coils, whereby a magnetic field (across the gap layer) is generated at the magnetic poles. Thus, information is written on a magnetic recording medium by the magnetic field.
A method of manufacturing a magnetic transducer of first aspect of the invention comprises the steps of: forming on a substrate a stack including an antiferromagnetic layer, a ferromagnetic layer, a nonmagnetic layer and a soft magnetic layer; and patterning the stack so that a distance between one end face of the antiferromagnetic layer and the opposite face is longer than at least a distance between one end face of the soft magnetic layer (on the side of the one end face of the antiferromagnetic layer) and the opposite face. According to the manufacturing method, obtained is the stack comprising the antiferromagnetic layer, the ferromagnetic layer, the nonmagnetic layer and the soft magnetic layer, which are formed on the substrate in this order.
In the method of manufacturing a magnetic transducer of first aspect of the invention, the antiferromagnetic layer, which has the longer distance between the one end face and the opposite face (than at least the soft magnetic layer), is formed. Joule""s heat generated by the current passing through the stack is dissipated through the antiferromagnetic layer.
Preferably, the patterning step uses ion milling. In this case, an angle of inclination of an inclined surface of the stack may be controlled by adjusting at least either an angle of incidence of ions for ion milling or a thickness of a resist mask.
A method of manufacturing a thin film magnetic head of first aspect of the invention comprising a magnetic transducer of the invention comprises: a step of forming the magnetic transducer including the steps of: forming on a substrate a stack including an antiferromagnetic layer, a ferromagnetic layer, a nonmagnetic layer and a soft magnetic layer; and patterning the stack so that a distance between one end face of the antiferromagnetic layer and the opposite face is longer than at least a distance between one end face of the soft magnetic layer (on the side of the one end face of the antiferromagnetic layer) and the opposite face.
Preferably, the method of manufacturing a thin film magnetic head of first aspect of the invention further comprises the steps of: forming a first magnetic shield layer; forming a first shield gap layer on the first magnetic shield layer; forming a magnetic transducer on the first shield gap layer; forming a second shield gap layer on the magnetic transducer; and forming a second magnetic shield layer on the second shield gap layer.
A magnetic transducer of second aspect of the invention comprises: a magneto-sensitive layer for sensing an external magnetic field; and a heat dissipation layer formed adjacent to the magneto-sensitive layer. Magneto-sensitive layers include, for example, a magnetoresistive film whose electrical resistance changes in accordance with the external magnetic field, and the like. Magnetoresistive films include, for example, an AMR film, a GMR film, a TMR film (a tunnel junction type magnetoresistive film), and so on. A state in which the layers are adjacent to each other refers to not only a state in which the layers are in direct contact with each other but also a state in which the layers adjoin each other with another layer in between.
The magnetic transducer of second aspect of the invention, Joule""s heat generated by the current passing through the magneto-sensitive layer is transferred by heat transfer or the like to peripheral components of the magnetic transducer through the heat dissipation layer formed adjacent to the magneto-sensitive layer.
Preferably, a thickness of the heat dissipation layer is from 1 nm to 100 nm inclusive. Thus, much heat dissipation effect is obtained, and symmetry of the plus output and the minus output of the output is improved. Moreover, the heat dissipation layer may be made of a nonmagnetic metal film (for example, containing Zr, Bi, Ta, Pt or Pd) having higher resistance than resistance of the magneto-sensitive layer. Since the heat dissipation layer is of high resistance, the sense current passing through the magneto-sensitive layer is prevented from being diverted to the heat dissipation layer. Moreover, a surface area of the heat dissipation layer may be larger than that of the magneto-sensitive layer. The larger the surface area of the heat dissipation layer is, the larger a contact area of the heat dissipation layer and the magneto-sensitive layer and a contact area of the heat dissipation layer and external components (the magnetic shield layers, etc.) are. The larger the contact areas become, the higher the efficiency of heat dissipation becomes. Moreover, a distance between one end face of the heat dissipation layer (the surface facing the external magnetic field) and the opposite face may be longer than a distance between one end face of the magneto-sensitive layer (the surface facing the external magnetic field) and the opposite surface. Moreover, an insulating layer may be provided between the magneto-sensitive layer and the heat dissipation layer. The insulating layer is located between the magneto-sensitive layer and the heat dissipation layer, whereby the sense current passing through the magneto-sensitive layer can be prevented from being diverted to the heat dissipation layer.
Moreover, the magneto-sensitive layer may comprise a magnetoresistive film whose electrical resistance changes in accordance with the external magnetic field. More particularly, the magnetoresistive film may comprise: a nonmagnetic layer; a soft magnetic layer formed adjacent to one surface of the nonmagnetic layer and having the orientation of magnetization freely changing in accordance with the external magnetic field; a ferromagnetic layer formed adjacent to the other surface of the nonmagnetic layer; and an antiferromagnetic layer formed adjacent to a surface of the ferromagnetic layer, the surface being opposite to a surface in contact with the nonmagnetic layer. When the magnetic field from the magnetic recording medium is applied to the soft magnetic layer, the orientation of magnetization of the soft magnetic layer is changed. Thus, electrical resistance changes in response to a relative angle between the changed orientation of magnetization of the soft magnetic layer and the (fixed) orientation of magnetization of the ferromagnetic layer. Consequently, the voltage change incident to the change in electrical resistance is detected. Joule""s heat generated by the current passing through the soft magnetic layer, the nonmagnetic layer and the ferromagnetic layer is transferred to the outside through the heat dissipation layer. The heat dissipation layer can be formed adjacent to the antiferromagnetic layer or the soft magnetic layer.
A thin film magnetic head of second aspect of the invention comprising a magnetic transducer, the magnetic transducer has any one of the above-described structures. Preferably, another thin film magnetic head of the invention comprises two magnetic shield layers located so as to face each other with the magnetic transducer in between, for magnetically shielding the magnetic transducer. Thus, Joule""s heat generated by the current passing through the magneto-sensitive layer of the magnetic transducer is transferred to one magnetic shield layer through the heat dissipation layer.
Moreover, the thin film magnetic head of second aspect of the invention may have: two magnetic layers magnetically coupled to each other and each having a recording-medium-facing part including a magnetic pole, the magnetic poles facing each other with a gap layer in between, the magnetic layers being each formed of at least one layer; and thin film coils arranged between the two magnetic layers. A current is passed through the thin film coils, whereby the magnetic field is generated at the magnetic poles. Therefore, information can be written on the magnetic recording medium by the magnetic field.
A method of manufacturing a magnetic transducer of second aspect of the invention comprises the step of forming the heat dissipation layer and the magneto-sensitive layer so that the heat dissipation layer and the magneto-sensitive layer are adjacent to each other.
Preferably, the method of manufacturing a magnetic transducer of second aspect of the invention comprises the steps of forming the heat dissipation layer on a base; and forming the magneto-sensitive layer on the heat dissipation layer. According to the manufacturing method, obtained is the magnetic transducer in which the heat dissipation layer and the magneto-sensitive layer are stacked on the substrate in this order. Moreover, another method of manufacturing a magnetic transducer of the invention may further comprise the step of forming another heat dissipation layer on the magneto-sensitive layer (formed on the heat dissipation layer). According to the manufacturing method, obtained is the magnetic transducer in which the heat dissipation layer, the magneto-sensitive layer and another heat dissipation layer are stacked on the substrate in this order. Moreover, another method of manufacturing a magnetic transducer of the invention may comprise the steps of: forming the magneto-sensitive layer on the base; and forming the heat dissipation layer on the magneto-sensitive layer. According to the manufacturing method, obtained is the magnetic transducer in which the magneto-sensitive layer and the heat dissipation layer are stacked on the sputtering, for example.
The method of manufacturing a magnetic transducer of second aspect of the invention may further comprise the step of: forming an insulating layer between the heat dissipation layer and the magneto-sensitive layer. According to the manufacturing method, obtained is the magnetic transducer having a structure in which the insulating layer is interposed between the heat dissipation layer and the magneto-sensitive layer. The insulating layer can be formed by, for example, oxidizing a surface of the heat dissipation layer.
A method of manufacturing a thin film magnetic head of second aspect of the invention, which is a method of manufacturing a thin film magnetic head with a magnetic transducer, comprises a step of forming the magnetic transducer by using any one of the above-described methods of manufacturing a magnetic transducer.
Preferably, the step of forming the magnetic transducer includes the steps of forming a first magnetic shield layer; forming a first shield gap layer on the first magnetic shield layer; forming a magnetic transducer on the first shield gap layer; forming a second shield gap layer on the magnetic transducer; and forming a second magnetic shield layer on the second shield gap layer is performed by using any one of the above-described methods of manufacturing a magnetic transducer.
Other and further objects, features and advantages of the invention will appear more fully from the following description.